(1) Field of the Invention
This invention relates to a fire detection device, and more particularly to a fire detection device for detecting a fire.
(2) Description of the Related Art
Conventionally, a fire detection device is put into practical use in the form of a device utilizing a thermograph, a radiation-based fire detection device, or a device using a visible light camera.
A thermograph recognizes an occurrence of a fire when it detects a temperature higher than 350xc2x0 C. The radiation-based fire detection device detects a radiation having a wavelength (e.g., 4.3 xcexcm) of an infrared ray to be emitted from flames and a radiation of a wavelength (e.g., 2.5 xcexcm) other than the wavelength of the infrared ray, and determines an occurrence of a fire based on the detected radiations. Further, the device using a visible light camera compares the luminance of each point of an image taken by the visible light camera with a predetermined threshold value, and extracts a portion of the image having detected luminance values higher than the predetermined threshold value, for determination of an occurrence of a fire.
On the other hand, a fire detection device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 11-134571 determines a variance of luminance for each pixel of an input image supplied by a camera, and discriminates a flame from noise based on a degree of the variance, to detect a fire.
However, these conventional fire detection devices suffer from the following problems: Although a thermograph provides a highly accurate fire detection, a sensor used for the thermograph is very expensive, so that this device cannot be widely used due to its high cost.
In the case of the radiation-based fire detection device, it uses a single element for a wide field of view, and is incapable of determining the location of a fire. Therefore, this device is not suitable for monitoring a wide area for fire detection.
Further, the device for detecting a fire by using a visible light camera can realize a high-accuracy detection in a site used for a limited purpose, such as the inside of a tunnel, where there occur only small changes in environmental conditions. However, at locations where environmental conditions undergo violent changes, such as outdoors, there is a fear of erroneous detections due to camera movement, the weather, etc. To cope with all environmental conditions, a complicated image processing is required.
On the other hand, in the case of discrimination of a flame from noise based on the degree of the variance, the setting of the predetermined threshold value is a critically important matter in designing of the device. However, in the prior art disclosed in the aforementioned Japanese Laid-Open Patent Publication (Kokai) No. 11-134571, the setting of the threshold value is not quantitatively determined, which makes it impossible to positively discriminate a moving flame from noise.
Further, in this conventional technique, the threshold value is qualitatively set for each point where fire detection is required, based on the measured variance conditions, and hence the conventional technique suffers from a poor working efficiency, and lack of flexibility.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a fire detection device which is capable of monitoring a wide area, and detecting a fire with efficiency and high accuracy, without necessitating a complicated image processing.
To attain the above object, there is provided a fire detection device for detecting a fire. The fire detection device is characterized by comprising luminance data extraction means for extracting luminance data from an input image, resampling means for carrying out resampling of the luminance data over a time period longer than a repetition period of movement of a flame, to generate resampled data, and fire detection means for calculating an average value of N (natural number equal to or larger than 2) items of the resampled data, and determining that the input image is an image of a flame, by comparison between a count of sampled data items larger than the average value or a count of sampled data items smaller than the average value and a predetermined value.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.